Add color output for SimplePrinter

Whether or not colored output is used is determined automatically. If you're not
happy with the autodetect you can override it by setting the property
`useColor`. This might happen when running in Tmux/screen in which Dart falsely
claims the terminal does not support ANSI escape codes.

Author: haarts

example/main.dart

@@ -24,4 +24,6 @@ void demo() {
   logger.e("Error! Something bad happened", "Test Error");
 
   loggerNoStack.v({"key": 5, "value": "something"});
+
+  Logger(printer: SimplePrinter()..useColor = true).v("boom");
 }

lib/src/printers/simple_printer.dart

@@ -1,4 +1,7 @@
 import 'dart:convert';
+import 'dart:io' as io;
+
+import 'package:io/ansi.dart';
 
 import 'package:logger/src/logger.dart';
 import 'package:logger/src/log_printer.dart';
@@ -17,19 +20,42 @@ class SimplePrinter extends LogPrinter {
     Level.wtf: '[WTF]',
   };
 
-  final bool printTime;
+  static final levelColors = {
+    Level.verbose: darkGray,
+    Level.debug: defaultForeground,
+    Level.info: blue,
+    Level.warning: yellow,
+    Level.error: magenta,
+    Level.wtf: red,
+  };
+
+  bool printTime;
+
+  /// You can override the auto detected color support with this property. This
+  /// is useful when Dart incorrectly reports a terminal not supporting colors.
+  /// This happens, for example, when running the Dart program under Tmux or
+  /// screen. See https://github.com/dart-lang/sdk/issues/31606.
+  bool useColor;
 
-  SimplePrinter({this.printTime = false});
+  SimplePrinter({this.printTime = false})
+      : useColor = io.stdout.supportsAnsiEscapes;
 
   @override
   List<String> log(LogEvent event) {
-    var messageStr = stringifyMessage(event.message);
+    var messageStr = _stringifyMessage(event.message);
     var errorStr = event.error != null ? "  ERROR: ${event.error}" : "";
     var timeStr = printTime ? "TIME: ${DateTime.now().toIso8601String()}" : "";
-    return ["${levelPrefixes[event.level]} $timeStr $messageStr$errorStr"];
+    return ["${_labelFor(event.level)} $timeStr $messageStr$errorStr"];
+  }
+
+  String _labelFor(Level level) {
+    var prefix = levelPrefixes[level];
+    var color = levelColors[level];
+
+    return overrideAnsiOutput(useColor, () => color.wrap(prefix));
   }
 
-  String stringifyMessage(dynamic message) {
+  String _stringifyMessage(dynamic message) {
     if (message is Map || message is Iterable) {
       var encoder = JsonEncoder.withIndent(null);
       return encoder.convert(message);

pubspec.yaml

@@ -7,6 +7,9 @@ homepage: https://github.com/leisim/logger
 environment:
   sdk: ">=2.1.0 <3.0.0"
 
+dependencies:
+  io: 0.3.3
+
 dev_dependencies:
   test: any
   pedantic: ^1.9.0

test/printers/simple_printer_test.dart

@@ -1,6 +1,8 @@
 import 'package:test/test.dart';
 import 'package:logger/logger.dart';
 
+const ansiEscapeLiteral = '\x1B';
+
 void main() {
   LogEvent event = LogEvent(
     Level.debug,
@@ -9,19 +11,45 @@ void main() {
     StackTrace.current,
   );
 
+  var plainPrinter = SimplePrinter()
+    ..useColor = false
+    ..printTime = false;
+
   test('represent event on a single line (ignoring stacktrace)', () {
-    var outputs = SimplePrinter().log(event);
+    var outputs = plainPrinter.log(event);
 
     expect(outputs, hasLength(1));
     expect(outputs[0], '[D]  some message  ERROR: some error');
   });
 
+  group('color', () {
+    test('print color', () {
+      // `useColor` is detected but here we override it because we want to print
+      // the ANSI control characters regardless for the test.
+      var printer = SimplePrinter()..useColor = true;
+
+      expect(printer.log(event)[0], contains(ansiEscapeLiteral));
+    });
+
+    test('toggle color', () {
+      var printer = SimplePrinter()..useColor = false;
+
+      expect(printer.log(event)[0], isNot(contains(ansiEscapeLiteral)));
+    });
+  });
+
   test('print time', () {
     var printer = SimplePrinter(printTime: true);
 
     expect(printer.log(event)[0], contains('TIME'));
   });
 
+  test('toggle time', () {
+    var printer = SimplePrinter(printTime: true)..printTime = false;
+
+    expect(printer.log(event)[0], isNot(contains('TIME')));
+  });
+
   test('omits error when null', () {
     LogEvent withoutError = LogEvent(
       Level.debug,
@@ -43,7 +71,7 @@ void main() {
     );
 
     expect(
-      SimplePrinter().log(withMap)[0],
+      plainPrinter.log(withMap)[0],
       '[D]  {"foo":123}  ERROR: some error',
     );
   });
@@ -57,7 +85,7 @@ void main() {
     );
 
     expect(
-      SimplePrinter().log(withIterable)[0],
+      plainPrinter.log(withIterable)[0],
       '[D]  [1,2,3,4]  ERROR: some error',
     );
   });